The invention relates to plastic insulators that are attached to anodes used in electrowinning cells, to ensure precise and positive separation at all times between the anodes and the adjacent cathodes, including during loading and removal of the cathodes, and also to prevent shorting between intermediate portions of the anodes and warped portions of the cathodes.
An electrowinning facility, particularly the type used for copper electrowinning, includes a large number of cells, typically 20 to 300. Typically, there are 25 to 80 equally spaced anodes in each cell, and a like number of cathodes alternately positioned between the anodes. The anodes are composed of lead, which may be about one-fourth of an inch to three-fourths of an inch thick, about 32 to 36 inches wide, and about 36 to 60 inches high, and weigh roughly in the range of 110 pounds to 700 pounds. They are spaced on about two inch centers in the electrowinning cell. The upper edge of a lead anode is typically soldered in a slot in a copper header bar, or may be welded to the header bar coated with lead. The cathodes consist of very thin sheets of copper which are only about one thirty-secondth of an inch thick, supported on copper cathode header bars. The electrowon copper is deposited on the thin cathode sheets, which periodically are lifted out of the electrowinning cell to harvest the copper, and then another set is reloaded into the cell. Because of the thinness and fragileness of the cathode sheets, warping of the cathodes is a very common problem. Such warping leads to electrical shorts between the anodes and cathodes, reducing the efficiency of the copper recovery process and increasing the amount of electrical current consumed by the process. These problems are well known in the copper electrowinning industry. Numerous attempts have been made to solve the problems. Decreasing the average spacing between anodes and cathodes increases the electrode efficiency of an electrowinning cell, but the extent to which this can be done is limited by losses in efficiency caused by consequent shorting between cathodes and anodes. To avoid such shorting, various insulators, have been proposed. One type of insulator extends downward along the length of the lead anodes. Use of this technique is time-consuming and expensive. With this device, each lead anode has to be removed from the cell, appropriate holes drilled through it, and pins or screws must be passed through the insulator and the holes in the anode to permanently fix the insulator elements to the opposed faces of the lead anode. U.S. Pat. No. 3,997,421 teaches use of spring loaded plastic clips that are attached to the bottom edges of the anodes. U.S. Pat. No. 3,997,421 illustrates an insulator that fits over the copper header bar and has pointed, symmetrical upper surfaces which tend to guide cathodes as they are being lowered into the cell between their respective anodes, and thereby avoid rubbing of lead coating from the anode header bar onto the copper sheets of the cathode. In the past, copper refining plants using soluble, impure copper anodes often have made use of three-eighths inch PVC pipe bent into the shape of a hairpin and draped over the top of the anode. Such anodes have no header bar. Such "hairpin" insulators generally extend downward to a level below the lower edge of the anode, and have breather holes at the top. They are normally unconnected at their lower ends, and thus do not form a closed loop around the body of the anode. Such hairpin insulators are draped over the soluble copper anode immediately after it is placed in a refining cell. The anode rapidly dissolves over a three to four week period of time. Then, the hairpin insulator is removed, the remnants of the old anode are removed, and a new soluble copper anode is positioned in the refining cell to replace the old one, and the hairpin insulators are again draped over the new anode. Those skilled in the art will appreciate that as a practical matter there is a great difference between the foregoing copper refining process and a copper electrowinning process. The refining process is one in which the copper in the impure anodes is electrotypically placed into solution and plated out with much higher purity onto adjacent cathodes, whereas in an electrowinning process copper is already in solution as a result of prior leaching process. The purpose and operation of an electrowinning cell is to electrotypically win the metal from the solution. In a refining cell, both the anodes and the cathodes are composed of copper; whereas in an electrowinning cell, the anode is made of a lead alloy, and the cathode is composed of electrowon copper. In electrowinning operations, there can be substantial loss of purity of the deposited copper cathode as a result of rubbing of the copper cathodes against the lead anodes during removal or insertion of the cathodes into the electrowinning cell.
Thus, an entirely different set of considerations apply to design of anode insulators for copper refining cells than for copper electrowinning cells.
Another type of commercially available anode insulator which is used in copper electrowinning cells is a similar hairpin shaped plastic tube which is inserted through a hole near the upper edge of the anode beneath the anode header bar. This insulator extends downward to a level slightly below the lower edge of the anode, and is often held in place by binding the legs together with wire, tape, or rubber bands. This insulator does not prevent contact of the cathode with the lead coating of the anode header bar, and moreover, installation of this type of anode insulator requires removal of the anode, drilling of the holes required. None of the above-described anode insulators completely solves the problems associated with close spacing of anodes and cathodes, none solves the problems caused by warping of the cathodes during cell operation, and none reliably avoids contamination of the cathodes by preventing contact with the lead of the anode or the lead coating of the anode header bar during cell operation and during loading and removal of the cathode. There remains an unmet need for an economical, reliable, easily installed insulator that substantially solves all of these problems.